The present invention relates to the production of micro-patterns using layer-by-layer (“LbL”) self-assembly techniques. More specifically, the present invention relates to the combination of LbL self-assembly techniques with lithographic techniques to produce micro-patterns.
It is well known to use lithography techniques to form micro-patterns on silicon substrates during the production of integrated circuits, micro-electrical-mechanical systems (MEMS), and other micro-devices. A more recent, but rapidly growing technology area is LbL self-assembly techniques. LbL self-assembly generally consists of providing a charged substrate and placing the substrate in a first polyion solution having a charge opposite the substrate, thereby forming a thin film of the first polyion on the substrate. The substrate may then be placed in a second polyion solution (having a charge opposite the first polyion), thereby forming a second thin film of the second polyion. This basic process can be greatly varied to create films of different thicknesses and formed of many different polyions. Examples of the LbL self-assembly process may be seen in references such as U.S. Pat. No. 6,479,146, which is incorporated by reference herein in its entirety.
Research has been directed toward forming micro-patterns using LbL self-assembly. This research has mostly been based on the microprinting technique in which a template is first fabricated by stamping two functional chemical groups on a flat substrate, wherein one of these functional groups is adhesion resisting and the other adhesion promoting toward the particles which will later be used to form the micro-pattern. Typically the desired micro-pattern is created on the stamp by lithographic or other means. The functional chemicals are stamped onto the flat substrate in shape of the micro-pattern formed on the stamp and nanoparticles are directed onto adhesion-promoting regions while they are repelled by adhesion-resisting regions. This method has been successful, but requires careful and sometimes restrictive selection of chemicals and strict control during the adhesion or absorption process. Moreover, this process tends to limit the number of different chemicals which can be used to structure the micro-pattern and due to the flexible nature of the stamp material, tends to limit the resolution consistently achievable. It would be a significant improvement in the art to provide a method of forming LbL micro-patterns which avoided these shortcomings. Other references dealing with LbL self-assembly include: Decher, G., Science, 227, 1232 (1997); Lvov Y., Decher, G., Mohwald H., Langmuir, 9, 481 (1993); M. Onda, Y. Lvov, K. Ariga, T. Kunitake; “Multiple layered functional thin films” U.S. Pat. No. 6,020,175, both of which are incorporated by reference herein.